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You just stick it on your skin and your craving for chocolate magically disappears. At least, that's the claim of researchers from St George's Hospital in London, who have developed an anti-craving patch with a difference.

Reuters reports that the patch emits a sweet vanilla smell, mixed with other, unrevealed, scents, and, researchers said, it has shown up well in diet trials.

Unlike nicotine patches, it is not absorbed through the skin.

Study leader Catherine Collins said the stick-on patch halved subjects' intake of chocolate, and also reduced consumption of sugar-based drinks.

Two hundred overweight volunteers were divided into three groups which were given a lemon or dummy patch, a vanilla patch or no patch. After four weeks the vanilla group had lost far more weight than the others, Reuters said. Early tests on obese people who wore the patch showed they lost about 2 kg.

Dr Collins said taste and aroma have a feedback on brain biochemistry fairly immediately to tell you to stop eating, but the experiment had never before been applied to obese patients. Very sweet smells release the mood chemical serotonin, which makes you feel good, and chocolate has the same effect.

It's a fascinating study, according to Dr Peter Clifton who is director of the Clinical Research Unit at CSIRO Health Science and Nutrition.

"The results make sense," he said. "We are profoundly influenced by what we detect with our senses, and it sounds reasonable that it could influence our eating habits," he said.

"It may work because vanilla is quite a sickly smell, and may make you feel disinclined to eat.

Like standing over a cooking pot for too long and then not wanting to eat dinner, he said, continual exposure to the smell of something sweet may fool your senses into thinking that you had already eaten a cake or chocolate.

"But I would be interested to see if the effect wears off. You might get habituated to the smell after a while," he said. "But it sounds reasonable - I don't think it's just a diet fad."

The research is being presented today at the 13th International Congress of Dietetics in Edinburgh, Scotland.

It is the first of five patches in production. The second is designed to reduced cravings for fatty potato chips and others claim to alleviate insomnia and pre-menstrual stress or PMS. The anti-chocolate patch will be released in Britain later this year.